Presently, in certain non-volatile, programmable memories, such as FLASH memories, program operation is done by channel hot electron injection. This requires that a relatively high current be available from the power supply, typically 1 mA for a single memory cell. In dual power supply memories this current is available from a higher voltage power supply, sometimes referred to as Vpp. However, the provision of an external high current supply is not suitable for many applications.
Internal current supplies based on a single voltage power supply, for example provided at, 5 V, such single voltage sometimes being referred to as Vdd, have been provided in the prior art. However, these supplies must provide stable performance over the entire Vdd and temperature range, and this has led to problems. State of the art charge pumps of this type are able to generate a voltage in the range of 6 V and a current in the range of 10 mA, using voltage doublers with n-channel MOS transistors as rectifying elements. A problem with these circuits is that the voltage drop across the MOS devices due to transistor Vt and body effect at these current levels creates undesirable power dissipation. To overcome these undesirable effects, more complicated circuits have been devised to bootstrap the gate of the rectifying elements, increasing the component count and circuit complexity.
Accordingly, it is desired to have an internal charge pump that provides high current, efficiently, at moderate voltages. Further, it is desired to have such a charge pump that is stable in the whole Vdd and temperature range in which the memory is expected to operate. The present invention provides such a charge pump.